Resonant-cavity light-emitting diode and optical transmission module using the light-emitting diode

ABSTRACT

A resonant-cavity light-emitting diode includes a semiconductor light-emitting layer sandwiched between an under and an upper semiconductor distributed Bragg reflector mirror layer, which are formed on the substrate, a light extracting section formed on the upper semiconductor distributed Bragg reflector mirror layer and having an opening to extract light from the semiconductor light-emitting layer, and a groove formed by removing portions of the semiconductor light-emitting layer, under and upper semiconductor distributed Bragg reflector mirror layers which lie in a peripheral portion of the opening of the light extraction section and reach the under semiconductor distributed Bragg reflector mirror layer, the inner wall of the groove being formed to reflect part of light emitted from the semiconductor light-emitting layer into the groove.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2001-079981, filed Mar.21, 2001, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a resonant-cavity light-emitting diodewhich emits light in a direction perpendicular to one main surface of asubstrate.

[0004] 2. Description of the Related Art

[0005] A resonant-cavity light-emitting diode is a light-emitting devicehaving a structure similar to that of a vertical-cavity surface emittinglaser and is operated with laser oscillation suppressed by setting thereflectance on the light-emitting side low appropriately. As this typeof light-emitting device, for example, a device disclosed in IEEEPHOTONICS TECHNOLOGY LETTERS, VOL. 10, NO. 12, pp. 1685 to 1687, Dec.12, 1998, is known.

[0006] The resonant-cavity light-emitting diode has features incomparison with a normal LED since it has a cavity structure that (1)the emission spectral line width is narrow, (2) the directivity ofemitted light is high, and (3) the carrier lifetime of spontaneousemission is short.

[0007] Therefore, the resonant-cavity light-emitting diode is extremelysuitably used as a transmission light source for an optical LAN and anoptical data link. It is a light transmission device which plays animportant role, particularly, in the transmission rate of approximately100 Mbps to 1 Gbps and the response characteristics thereof largelydepend on the device size.

[0008] That is, as the device size becomes smaller, the carrier densityof an active layer caused when the same amount of current is injectedtherein becomes higher, and the carrier lifetime which controls theresponse characteristics of the light-emitting diode becomes shorter asthe carrier density becomes higher. Therefore, generally, the responsecharacteristics of the device become higher as the device size becomessmaller.

[0009] However, a reduction in the device size means that thelight-emitting area of the device is made small and there occurs aproblem that light output power is lowered accordingly as the devicesize is reduced.

[0010] One of the main factors in lowering the light output power due toreduction in the device size is considered as follows. That is, sincethe resonant-cavity light-emitting diode is a device which emits lightin a direction perpendicular to one main surface of the substrate on aflat plate, the light-emitting area on the main surface of the substrateis reduced with reduction in the device size. Therefore, the ratio ofthe area on the substrate side surface to the plane area of an effectiveactive region which contributes to light emission becomes higher and therate of light leaking into the substrate side surface side becomeshigher.

[0011] Thus, the conventional resonant-cavity light-emitting diode has aproblem that the light output power is lowered if the device size isreduced in order to enhance the response characteristics of the device.Therefore, it is required to realize a resonant-cavity light-emittingdiode which generates high light output power and is excellent in itsresponse characteristics.

BRIEF SUMMARY OF THE INVENTION

[0012] A resonant-cavity light-emitting diode according to a firstaspect of this invention comprises a substrate having first and secondmain surfaces which are substantially parallel to each other, a firstsemiconductor distributed Bragg reflector mirror layer formed on thefirst main surface of the substrate, a semiconductor light-emittinglayer formed over the first semiconductor distributed Bragg reflectormirror layer, a second semiconductor distributed Bragg reflector mirrorlayer formed over the semiconductor light-emitting layer, alight-extracting section which is formed on the second semiconductordistributed Bragg reflector mirror layer and having an opening toextract light from the semiconductor light-emitting layer, a firstelectrode formed around the opening of the light-extracting section onthe second semiconductor distributed Bragg reflector mirror layer, asecond electrode formed on the second main surface of the substrate, thesecond electrode being configured to form a current path leading to thefirst electrode through the first semiconductor distributed Braggreflector mirror layer, semiconductor light-emitting layer and secondsemiconductor distributed Bragg reflector mirror layer, and a reflectorportion provided on an inner wall of a groove, the groove being formedby removing portions of the first semiconductor distributed Braggreflector mirror layer, semiconductor light-emitting layer and secondsemiconductor distributed Bragg reflector mirror layer which lie in aperipheral portion of the first electrode and formed to penetratethrough each of the semiconductor light-emitting layer and secondsemiconductor distributed Bragg reflector mirror layer and reach thefirst semiconductor distributed Bragg reflector mirror layer, thereflector portion being formed to reflect part of light emitted from thesemiconductor light-emitting layer into the groove.

[0013] A resonant-cavity light-emitting diode according to a secondaspect of this invention comprises a substrate having first and secondmain surfaces which are substantially parallel to each other, a firstsemiconductor distributed Bragg reflector mirror layer formed on thefirst main surface of the substrate, a semiconductor light-emittinglayer formed over the first semiconductor distributed Bragg reflectormirror layer, a second semiconductor distributed Bragg reflector mirrorlayer formed over the semiconductor light-emitting layer, alight-extracting section which is formed on the second semiconductordistributed Bragg reflector mirror layer and has an opening to extractlight from the semiconductor light-emitting layer, a first electrodeformed around the opening of the light-extracting section on the secondsemiconductor distributed Bragg reflector mirror layer, a secondelectrode formed on the second main surface of the substrate, the secondelectrode being configured to form a current path leading to the firstelectrode through the first semiconductor distributed Bragg reflectormirror layer, semiconductor light-emitting layer and secondsemiconductor distributed Bragg reflector mirror layer, and a reflectorportion provided on an inner wall of a groove, the groove being formedby removing portions of the first semiconductor distributed Braggreflector mirror layer, semiconductor light-emitting layer and secondsemiconductor distributed Bragg reflector mirror layer which lie in aperipheral portion of the first electrode and formed to penetratethrough each of the semiconductor light-emitting layer and secondsemiconductor distributed Bragg reflector mirror layer and reach thefirst semiconductor distributed Bragg reflector mirror layer, thereflector portion being formed to reflect part of light emitted from thesemiconductor light-emitting layer into the groove, and ahigh-resistance region which is formed to reach the inner wall of thegroove and formed by making portions of the first and secondsemiconductor distributed Bragg reflector mirror layers other than atleast portions thereof which lie under and below the light-extractingsection electrically highly resistive.

[0014] An optical transmission module according to a third aspect ofthis invention comprises a resonant-cavity light-emitting diodeaccording to the first aspect and an optical fiber on which light fromthe light-extracting section and groove of the resonant-cavitylight-emitting diode is incident.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0015]FIG. 1 is a cross-sectional view showing the structure of aresonant-cavity light-emitting diode according to a first embodiment ofthis invention,

[0016]FIG. 2 is a top view showing the resonant-cavity light-emittingdiode according to the first embodiment,

[0017]FIG. 3 is a light emission characteristic diagram which exhibitsthe effect of this invention,

[0018]FIG. 4 is a cross-sectional view showing the structure of aresonant-cavity light-emitting diode according to a second embodiment ofthis invention,

[0019]FIG. 5 is a top view showing the resonant-cavity light-emittingdiode according to the second embodiment,

[0020]FIG. 6 is a cross-sectional view showing the structure of aresonant-cavity light-emitting diode according to a third embodiment ofthis invention, and

[0021]FIG. 7 is a cross-sectional view showing the main portion of anoptical transmission module according to a fourth embodiment of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] In a resonant-cavity light-emitting diode according to a firstaspect of this invention, a groove which reaches a first (lower)semiconductor distributed Bragg reflector mirror layer is formed in aperipheral portion of a first electrode (on the light-emitting surfaceside). Therefore, part of the light emitted from a semiconductorlight-emitting layer which leaks in a direction toward the side surfaceof the device (that is, in a direction different from the thicknessdirection of the semiconductor light-emitting layer) is emitted into thegroove through a portion near the inner wall of the groove which lies onthe first electrode side, repeatedly reflected from the inner wallsurface of the groove and propagated in a direction toward the frontsurface of the device in which the groove is opened.

[0023] As a result, a large portion of light which is transmitted to theside surface of the semiconductor light-emitting layer and has beenattenuated inside the conventional device can be effectively extractedin the resonant-cavity light-emitting diode with the above structure andthe light output power of the device can be increased.

[0024] Further, in a resonant-cavity light-emitting diode according toanother aspect of this invention, portions of first (lower) and second(upper) semiconductor distributed Bragg reflector mirror layers exceptat least portions of the above layers which lie under and below thelight-extracting section are made electrically highly resistive, and thehighly resistive portions of the first and second semiconductordistributed Bragg reflector mirror layers are formed to reach the innerwall of the groove.

[0025] In a resonant-cavity light-emitting diode with the abovestructure, since the groove which reaches the first semiconductordistributed Bragg reflector mirror layer is formed in the peripheralportion of a first electrode, part of the light emitted from thesemiconductor light-emitting layer which leaks in a direction toward theside surface of the device (that is, in a direction different from thethickness direction of the semiconductor light-emitting layer) isemitted or radiated into the groove through a portion near the innerwall of the groove which lies on the first electrode side, repeatedlyreflected from the inner wall surface of the groove and propagated in adirection toward the front surface of the device in which the groove isopened.

[0026] As a result, as in the resonant-cavity light-emitting diode ofthe first aspect, the light output power of the device can be increased.Further, since part of the inner wall surface of the groove is madehighly resistive, a leakage current will not flow along the surface ofthe inner wall of the groove. Therefore, even if a protection film toprevent deterioration of the inner wall surface of the groove is notformed on the inner wall surface, a highly reliable device can beattained.

[0027] There will now be described embodiments of this invention withreference to the accompanying drawings.

[0028] (First Embodiment)

[0029] A first embodiment of this invention is a red resonant-cavitylight-emitting diode having a light emission wavelength of approximately665 nm and using an InGaAlP-based multiple quantum well structure as anactive layer.

[0030]FIG. 1 is a cross-sectional view showing the schematic structureof a resonant-cavity light-emitting diode 100 according to the firstembodiment. FIG. 2 shows the schematic structure of the top surface ofthe resonant-cavity light-emitting diode 100 shown in FIG. 1. The crosssection taken along the 1-1 line in FIG. 2 corresponds to FIG. 1.

[0031] In the resonant-cavity light-emitting diode 100 according to thefirst embodiment, an n-type AlGaAsbased distributed Bragg reflectormirror 107 is formed on one main surface of an n-type GaAs substrate108. The distributed Bragg reflector mirror is hereinafter referred toas a DBR mirror.

[0032] It is preferable to use a substrate which has a plane orientation(100) and whose axis is shifted by 10° to 15° as the GaAs substrate 108.This is applied to the embodiments described below.

[0033] On the DBR mirror 107, an n-type InGaAlP cladding layer 106, anInGaAlP-based multiple quantum well active layer 105 which is adjustedto have a light emission peak wavelength of 655 nm, a p-type InGaAlPcladding layer 104, an AlGaAs-based p-type DBR mirror 103 and a p-typeGaAs contact layer 102 are sequentially grown by an MOCVD (metal organicchemical vapor deposition) method. The total optical film thickness ofthe cladding layers and multiple quantum well active layer is set to becoincident with the resonant wavelength (665 nm).

[0034] In the AlGaAs-based DBR mirrors 103 and 107, a structure in whichlayers of Al₀₉₈Ga_(0.02)As and Al_(0.5)Ga_(0.5)As are alternatelyaccumulated and the optical film thickness of each later is set to be ¼the resonant wavelength (665 nm).

[0035] In the n-side DBR mirror layer 107, a structure in which layersare repeatedly accumulated 30.5 times starting from Al_(0.98)Ga_(0.02)Asand in which the final layer is formed of Al_(0.98)Ga_(0.02)As is used.On the other hand, in the p-side DBR mirror layer 103, a structure inwhich layers are repeatedly accumulated 10 times starting fromAl_(0.98)Ga_(0.02)As and in which the final layer is formed ofAl_(0.5)Ga_(0.5)As is used. Thus, the resonant wavelength of a cavitystructure configured by the DBR mirrors below and above the active layeris set to 665 nm.

[0036] Further, in a region except a circular region having a diameterof 70 μm which is used as a light-emitting region, protons areselectively ion-implanted to form a high-resistance region 110 and acurrent confinement portion is provided. At this time, the condition forion-implantation is that the acceleration energy is 200 keV and the doseis 1×10¹⁵ cm⁻².

[0037] A p-side electrode 101 having a pattern as shown in FIG. 2 and abonding pad 101 a are formed on the surface of the p-type GaAs contactlayer 102 which is the top layer of the semiconductor layers. As shownin the drawing, in the p-side electrode 101, a circular opening portionwith a diameter of 60 μm is formed directly above the light-emittingregion in order to extract light.

[0038] Further, a portion surrounding the p-side electrode 101 andbonding pad 101 a is selectively etched in the GaAs substrate 108 toform a groove 111 having a substantially a U-shaped cross section.

[0039] A ring-like groove which is formed in the peripheral portion ofthe p-side electrode 101 surrounding at least the opening portion isformed to have a concave surface to reflect, in the groove, light whichis part of light emitted from the current injection region lying belowthe opening portion of the p-side electrode 101 and which spreads in adirection toward the side surface of the device, and direct the lighttoward the front surface side of the device on which the p-sideelectrode 101 is provided while repeatedly reflecting the light asdescribed above. The inner and outer diameters of the ring-like grooveare respectively set to 100 μm and 140 μm, for example.

[0040] The cross section of the ring-like groove is not limited tosubstantially a U-shape, but may be set as a V-shape, and if the widththereof is made smaller in a portion nearer to the bottom of the groove,light can be efficiently extracted toward the front surface side.However, in order to direct light which spreads in a direction towardthe side surface of the device to the front surface side of the deviceon which the p-side electrode 101 is provided, the ring-like groove isrequired to be formed with an inner sidewall portion 111 a having thesurface state described below and an outer sidewall portion 111 bconfigured by the semiconductor layers left behind on the outer portionof the groove 111.

[0041] That is, the outer sidewall portion 111 b is required to be areflector which has such a surface state as to reflect light spreadingtoward the side surface of the device into the groove 111 or efficientlyreflect the light toward the front surface side of the device.

[0042] On the other hand, the inner sidewall portion 111 a is requiredto emit light which spreads toward the side surface of the device intothe groove 111. In addition, when light emitted into the groove 111 isreflected from the outer sidewall portion 111 b at an angle at which thelight is incident on the inner sidewall portion 111 a, the innersidewall portion 111 a is required to have such a surface state as tofurther reflect the light into the groove 111 or efficiently reflect thelight toward the front surface side of the device.

[0043] In order to attain the surface states of the inner sidewallportion 111 a and outer sidewall portion 111 b, the smoothness of thesurface in the groove 111, the inclinations of the portions extendingfrom the bottom portion to the upper ends of the inner sidewall portion111 a and outer sidewall portion 111 b, the curvatures of the surfacesof the inner sidewall portion 111 a and outer sidewall portion 111 b andthe like are controlled in an adequate etching condition by taking thereflection effect into consideration.

[0044] Since the groove is formed in a ring-like form in the peripheralportion of the p-side electrode 101, it becomes possible to emit lightin all directions toward the side surface of the semiconductorlight-emitting layer and efficiently extract the light toward the frontsurface side of the device.

[0045] The rear surface of the n-type GaAs substrate 108 is subjected toa rear-surface polishing process and an n-side electrode 109 is formedon the entire rear surface.

[0046] In the thus-formed resonant-cavity light-emitting diode, sincelight which spreads toward the side surface of the device can beefficiently directed toward the front surface side of the device andextracted, the light output power can be increased.

[0047]FIG. 3 shows the light emission characteristics of theresonant-cavity light-emitting diode shown in FIG. 1 and theconventional resonant-cavity light-emitting diode in which the currentis confined in a circular region of 70 μm. The curve formed by circulardots indicates the first embodiment and the curve formed by square dotsindicates the light emission characteristics of a conventionalresonant-cavity light-emitting diode. In the resonant-cavitylight-emitting diode of the first embodiment in which a groove 111 isformed, it is confirmed that the light output power is increased by 20%at a current of 25 mA in comparison with the conventional case.

[0048] (Second Embodiment)

[0049] As in the first embodiment, a second embodiment is a redresonant-cavity light-emitting diode having a light emission wavelengthof approximately 665 nm and using an InGaAlP-based multiple quantum wellstructure as an active layer.

[0050]FIG. 4 is a cross-sectional view showing the schematic structureof a resonant-cavity light-emitting diode 200 according to the secondembodiment. FIG. 5 shows the schematic structure of the top surface ofthe resonant-cavity light-emitting diode 200 shown in FIG. 4. The crosssection taken along the 4-4 line in FIG. 5 corresponds to FIG. 4.

[0051] The resonant-cavity light-emitting diode 200 according to thesecond embodiment is different from that of the first embodiment in thata metal reflection film 213 which reflects light is provided on an outersidewall portion 211 b of a groove 211, the groove 211 is formed in aclosed ring form, and an SiO₂ film 212 is provided in the groove 211 andthe other structure is similar to that of the first embodiment.

[0052] Therefore, in the resonant-cavity light-emitting diode 200according to the second embodiment, an n-type AlGaAs-based DBR mirror207, an n-type InGaAlP cladding layer 206, an InGaAlP-based multiplequantum well active layer 205, a p-type InGaAlP cladding layer 204, anAlGaAs-based p-type DBR mirror 203, a p-type GaAs contact layer 202 anda current confinement portion formed of a high-resistance region 210 areprovided on one main surface of an n-type GaAs substrate 208. Further,an n-side electrode 209 is formed on the entire portion of the polishedrear surface of the n-type GaAs substrate 208.

[0053] In the second embodiment, a ring-form groove 211 having an innerdiameter of 100 μm and an outer diameter of 140 μm is concentricallyformed with respect to the current confinement portion from the surfaceof the p-type GaAs contact layer 202 by etching in the structure havinga portion which ranges from the p-type GaAs contact layer 202 to thecurrent confinement portion formed of the high-resistance region 210 andis formed in the same manner as in the first embodiment.

[0054] After the groove 211 is formed, the surface in the groove 211 andthe surface of the p-type GaAs contact layer 202 are covered with anSiO₂ film 212 deposited by the CVD (Chemical Vapor Deposition) method.However, at least in a range of the diameter of 70 μm on the currentconfinement portion surrounded by the high-resistance region 210, theSiO₂ film 212 is partly removed in a circular form and the surface ofthe p-type GaAs contact layer 202 is exposed and used as an emittedlight extraction portion.

[0055] Further, on the surface of the p-type GaAs contact layer 202, aring-form p-side electrode 201 having an inner diameter of 60 μm and anouter diameter of 80 μm in the surface region is formed as a metal layerof TiPtAu, for example. In the second embodiment, the diameter of thecurrent confinement portion is set to 62 μm.

[0056] The metal reflection film 213 which reflects light and isprovided on the outer sidewall portion 211 b of the groove 211 and abonding pad 201 a having a connecting portion 201 b used for connectionwith the p-side electrode 201 and provided on the SiO₂ film 212 whichlies outside the groove 211 are formed as metal layers of TiPtAu, forexample.

[0057] The groove 211, p-side electrode 201, metal reflection film 213and emitted light extraction portion are arranged concentrically withrespect to the current confinement portion, but the metal layers of thep-side electrode 201, metal reflection film 213, bonding pad 201 a andconnecting portion 201 b can be simultaneously formed by the followinglift-off method.

[0058] That is, a resist film is first formed on a region on which theabove metal film is not formed. The region on which the above metal filmis not formed contains the emitted light extraction portion in which thesurface of the p-type GaAs contact layer 202 on the current confinementportion is exposed, a portion on the SiO₂ film 212 which lies outsidethe peripheral edge (at a distance of 40 μm from the center of thering-form electrode) of the p-side electrode 201, the inner sidewallportion 211 a of the groove 211, and a portion on the SiO₂ film 212which lies outside the groove 211 and from which a forming region of thebonding pad 201 a and connecting portion 201 b is omitted. After this, aTiPtAu layer is formed on the entire surface. In this state, by removingthe resist layer together with the metal films formed thereon, the metalfilms are simultaneously patterned.

[0059] Finally, as in the case of the first embodiment, the rear surfaceis polished and an n-side electrode 209 is formed thereon.

[0060] As in the first embodiment, in the above resonant-cavitylight-emitting diode 200, the light extraction efficiency can beenhanced by use of the groove 211. Further, since the metal reflectionfilm 213 using the same metal layer as the p-side electrode 201 isformed on the outer sidewall portion 211 b of the ring-form groove 211,light emitted into the groove is reflected from the reflection film onthe inner wall of the groove and light in the groove is prevented frombeing incident on the internal portion of the semiconductor layersaround the groove. Since the metal reflection film 213 is provided, thereflectance on the outer sidewall surface 211 b of the groove 211becomes higher than that in the first embodiment and it becomes possibleto extract more efficiently light emitted into the groove toward thefront surface side of the device.

[0061] (Third Embodiment)

[0062]FIG. 6 is a cross-sectional view showing the schematic structureof a resonant-cavity light-emitting diode 300 according to a thirdembodiment of this invention. As in the first embodiment, the thirdembodiment is also a red resonant-cavity light-emitting diode having alight emission wavelength of approximately 665 nm and using anInGaAlP-based multiple quantum well structure as an active layer.

[0063] In the resonant-cavity light-emitting diode 300 according to thethird embodiment, an n-type AlGaAs-based DBR mirror 307, an n-typeInGaAlP cladding layer 306, an InGaAlP-based multiple quantum wellactive layer 305 which is adjusted to have a light emission peakwavelength of 655 nm, a p-type InGaAlP cladding layer 304, anAlGaAs-based p-type DBR mirror 303 and a p-type GaAs contact layer 302are sequentially grown on one main surface of an n-type GaAs substrate308 by an MOCVD method. The total optical film thickness of the claddinglayers and multiple quantum well active layers is set to be coincidentwith the resonant wavelength (665 nm).

[0064] In the AlGaAs-based DBR mirrors 303 and 307, a structure in whichlayers of Al_(0.98)Ga_(0.02)As and Al_(0.5)Ga_(0.5)As are alternatelyaccumulated and the optical film thickness of each layer is set to be ¼the resonant wavelength (665 nm).

[0065] In the n-side DBR mirror layer 307, the layers ofAl_(0.98)Ga_(0.02)As and Al_(0.5)Ga_(0.5)As are repeatedly accumulated30 times starting from Al_(0.98)Ga_(0.02)As, and the last layer of theDBR mirror layer 307 closest to the InGaAlP-based multiple quantum wellactive layer 305 is formed of an AlAs layer which forms a selectivelyoxidized layer 310, as will be described later.

[0066] On the other hand, in the p-side DBR mirror layer 303, astructure is used in which the first layer thereof closest to theInGaAlP-based multiple quantum well active layer 305 is formed of anAlAs layer which forms the selectively oxidized layer 310, and thelayers of Al_(0.98)Ga_(0.02)As and Al_(0.5)Ga_(0.5)As are repeatedlyaccumulated 9.5 times starting from Al_(0.5)Ga_(0.5)As, the last layerbeing formed of Al_(0.5)Ga_(0.5)As. Thus, the resonant wavelength of acavity structure configured by the DBR mirrors below and above theactive layer is set to 665 nm.

[0067] The respective semiconductor layers ranging from the surface ofthe p-type GaAs contact layer 302 which is the top layer of thesemiconductor layers to the GaAs substrate 308 are selectively etched toform a ring-form groove 311 with a substantially U-shaped cross sectionhaving an inner diameter of 100 μm and an outer diameter of 140 μm inthe surface of the p-type GaAs contact layer 302.

[0068] Further, each of the AlAs layers formed in the DBR mirrors aboveand below the active layer is oxidized in a lateral direction from theexposed portion of the groove 311 by heat treatment in the vaporatmosphere, and is formed into the selectively oxidized layer 310 in aregion except for a circular region having a diameter of 70 μm from thecenter of the ring-form groove 311, and a current confinement portion isprovided.

[0069] After the selectively oxidized layers 310 are formed, the surfacein the groove 311 and the surface of the p-type GaAs contact layer 302are covered with an SiO₂ film 312 deposited by the CVD method. However,at least in a range with a diameter of 70 μm on the current confinementportion surrounded by the selectively oxidized layers 310, the SiO₂ film312 is partly removed in a circular form and the surface of the p-typeGaAs contact layer 302 is exposed and used as an emitted lightextraction portion.

[0070] Further, around the emitted light extraction portion on thesurface of the p-type GaAs contact layer 302, a ring-form p-sideelectrode 301 having an inner diameter of 60 μm and an outer diameter of80 μm in the surface region and a bonding pad having a connectingportion for connection with the p-side electrode 301 on the SiO₂ film312 which lies outside the groove 311 are each formed as a metal layerof TiPtAu, for example. Finally, the rear surface is polished and ann-side electrode 309 is formed thereon.

[0071] As in the first embodiment, in the above resonant-cavitylight-emitting diode 300, the light extraction efficiency can beenhanced by use of the groove 311. Further, since the refractive indexof the selectively oxidized layers 310 of the AlAs layers provided aboveand below the light emission layer is small, light emitted into betweenthe upper and lower selectively oxidized layers 310 is confined in aspace between the two selectively oxidized layers 310 and can beefficiently extracted from the groove 311 to the outside.

[0072] In the first to third embodiments, the diameter of the currentconfinement potion is set to 62 to 70 μm, but it is not limited to theabove values and can be selectively set in a range of 30 to 100 μm. Ifthe diameter is smaller than 30 μm, the light output power becomesinsufficient, and if the diameter is larger than 100 μm, the responsespeed becomes low. Therefore, it is preferable to set the diameter ofthe current confinement potion to 50 to 80 μm.

[0073] Further, it is preferable to set the inner diameter of the groovesurrounding the current confinement portion to a value obtained byadding 30 μm to the selected diameter of the current confinement portionand set the outer diameter of the groove to a value obtained by adding40 μm to the inner diameter thereof (that is, the groove width of 20μm).

[0074] The size of the light emission diode chips 100, 200, and 300 isapproximately 300 μm×(200 to 250) μm.

[0075] Further, as the material of the semiconductor light emissionlayer, a material of In_(1−x)(Ga_(1−y)Al_(y))_(x)P (0≦x, y≦1) can beused and the light emission wavelength can be selected in a range of 620to 690 nm.

[0076] (Fourth Embodiment)

[0077] A fourth embodiment is an optical transmission module obtained bycombining the red resonant-cavity light-emitting diode according to oneof the first to third embodiments and a plastic optical fiber.

[0078]FIG. 7 is a cross-sectional view showing the main structure of anoptical coupler of the optical transmission module according to thefourth embodiment. A red resonant-cavity light-emitting diode 704 havinga light extraction groove formed therein and described in the first tothird embodiments is mounted on a sub-mount 703 which is also used as aheat sink and incorporated into a package 702.

[0079] A plastic optical fiber 701 formed to extend from directly abovethe red resonant-cavity light-emitting diode 704 in a direction oppositeto the sub-mount 703 is optically aligned and coupled with the package702 so that the center of light emitted from the red resonant-cavitylight-emitting diode 704 will coincide with the central axis of a coresection 701 a.

[0080] The chip size of the red resonant-cavity light-emitting diode 704incorporated in the optical transmission module is approximately 250μm×310 μm, and the diameter of the emitted light extraction portion of ap-side electrode is 70 μm and the outer diameter of the groovesurrounding the peripheral portion thereof is 150 μm.

[0081] A multi-step index type fiber is used as the plastic opticalfiber 701. The core diameter of the multi-step index type plasticoptical fiber is 700 μm and the outer diameter of a cladding portion 701b is 750 μm.

[0082] Therefore, the core diameter of the plastic optical fiber isequal to or larger than four times the total diameter of the lightemission portion containing the groove of the red resonant-cavitylight-emitting diode 704 and a sufficiently large portion of lightemitted from the red resonant-cavity light-emitting diode 704 toward theplastic optical fiber 701 is incident on the core portion 701 a.

[0083] Further, since the plastic optical fiber has a small loss in thered wavelength band, the combination thereof with the redresonant-cavity light-emitting diode of the first to third embodimentsbecomes suitable.

[0084] In the optical transmission module with the above structure, thetransmission distance can be made longer with an increase in the lightoutput power of a light source in comparison with a conventional opticaltransmission module using a light-emitting diode. In FIG. 7, only themain structure of the optical coupler used as the module is shown, butoptical parts such as a driving IC and lens, mold resin and the like canbe contained as constituent elements.

[0085] In each of the above embodiments, the red resonant-cavitylight-emitting diode is explained, but this invention is not limited tored light and can be applied to resonant-cavity light-emitting diodes ofvarious light emission wavelengths.

[0086] As described above, according to the embodiments, since thegroove which reaches the DBR mirror on the substrate side is formed inthe peripheral portion of the light emission region of theresonant-cavity light-emitting diode, light which is part of lightemitted by current injection and spreads in a direction toward the sidesurface of the device can be extracted toward the front surface side ofthe device via the groove. Thus, the light extraction efficiency of theresonant-cavity light-emitting diode is improved and the light outputpower is increased.

[0087] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A resonant-cavity light-emitting diode comprising: a substrate having a first main surface and a second main surface which are substantially parallel to each other, a first semiconductor distributed Bragg reflector mirror layer formed on said first main surface of said substrate, a semiconductor light-emitting layer formed over said first semiconductor distributed Bragg reflector mirror layer, a second semiconductor distributed Bragg reflector mirror layer formed over said semiconductor light-emitting layer, a light extraction section which is formed on said second semiconductor distributed Bragg reflector mirror layer and has an opening to extract light from said semiconductor light-emitting layer, a first electrode formed around said opening of said light extraction section on said second semiconductor distributed Bragg reflector mirror layer, a second electrode formed on said second main surface of said substrate, said second electrode being configured to form a current path leading to said first electrode through said first semiconductor distributed Bragg reflector mirror layer, said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer, and a reflector portion provided on an inner wall of a groove, said groove being formed by removing portions of said first semiconductor distributed Bragg reflector mirror layer, said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer which lie in a peripheral portion of said first electrode and formed to penetrate through each of said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer and reach said first semiconductor distributed Bragg reflector mirror layer, said reflector portion being formed to reflect part of light emitted from said semiconductor light-emitting layer into said groove.
 2. The resonant-cavity light-emitting diode according to claim 1, wherein said reflector portion is configured with a concave surface with respect to light from said semiconductor light-emitting layer.
 3. The resonant-cavity light-emitting diode according to claim 2, wherein said groove has substantially a U-shaped cross section.
 4. The resonant-cavity light-emitting diode according to claim 1, wherein said groove is formed in substantially a ring form in a peripheral portion of said first electrode.
 5. The resonant-cavity light-emitting diode according to claim 1, wherein said reflector portion comprises a reflection film which is formed on said inner wall of said groove and reflects light from said semiconductor light-emitting layer.
 6. The resonant-cavity light-emitting diode according to claim 1, wherein said semiconductor light-emitting layer includes an active layer using an In_(1−x)(Ga_(1−y)Al_(y))_(x)P-series material (0≦x, y≦1) and a light emission wavelength thereof is 620 to 690 nm.
 7. A resonant-cavity light-emitting diode comprising: a substrate having a first main surface and a second main surface which are substantially parallel to each other, a first semiconductor distributed Bragg reflector mirror layer formed on said first main surface of said substrate, a semiconductor light-emitting layer formed over said first semiconductor distributed Bragg reflector mirror layer, a second semiconductor distributed Bragg reflector mirror layer formed over said semiconductor light-emitting layer, a light extraction section which is formed on said second semiconductor distributed Bragg reflector mirror layer and has an opening to extract light from said semiconductor light-emitting layer, a first electrode formed around said opening of said light extraction section on said second semiconductor distributed Bragg reflector mirror layer, a second electrode formed on said second main surface of said substrate, said second electrode being configure to form a current path leading to said first electrode through said first semiconductor distributed Bragg reflector mirror layer, said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer, a reflector portion provided on an inner wall of a groove, said groove being formed by removing portions of said first semiconductor distributed Bragg reflector mirror layer, said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer which lie in a peripheral portion of said first electrode and formed to penetrate through each of said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer and reach said first semiconductor distributed Bragg reflector mirror layer, said reflector portion of said groove being formed to reflect part of light emitted from said semiconductor light-emitting layer into said groove, and a high-resistance region which is formed to reach said inner wall of said groove and formed by making portions of said first semiconductor distributed Bragg reflector mirror layer and said second semiconductor distributed Bragg reflector mirror layer other than at least portions thereof which lie just below said opening of said light extraction section electrically highly resistive.
 8. The resonant-cavity light-emitting diode according to claim 7, wherein each of said first semiconductor distributed Bragg reflector mirror layer and said second semiconductor distributed Bragg reflector mirror layer includes a semiconductor layer with a high Al composition ratio and said high-resistance region is formed by selectively oxidized part of said semiconductor layer in a lateral direction from said groove.
 9. The resonant-cavity light-emitting diode according to claim 7, wherein said reflector portion is configured with a concave surface with respect to light from said semiconductor light-emitting layer.
 10. The resonant-cavity light-emitting diode according to claim 9, wherein said groove has substantially a U-shaped cross section.
 11. The resonant-cavity light-emitting diode according to claim 7, wherein said groove is formed in substantially a ring form in a peripheral portion of said first electrode.
 12. The resonant-cavity light-emitting diode according to claim 7, wherein said reflector portion comprises a reflection film which is formed on said inner wall of said groove and reflects light from said semiconductor light-emitting layer.
 13. The resonant-cavity light-emitting diode according to claim 7, wherein said semiconductor light-emitting layer includes an active layer using an In_(1−x)(Ga_(1−y)Al_(y))_(x)P-series material (0≦x, y≦1) 110 and a light emission wavelength thereof is 620 to 690 nm.
 14. An optical transmission module comprising: a resonant-cavity light-emitting diode, said resonant-cavity light-emitting diode including: a substrate having a first main surface and a second main surface which are substantially parallel to each other, a first semiconductor distributed Bragg reflector mirror layer formed on said first main surface of said substrate, a semiconductor light-emitting layer formed over said first semiconductor distributed Bragg reflector mirror layer, a second semiconductor distributed Bragg reflector mirror layer formed over said semiconductor light-emitting layer, a light extraction section which is formed on said second semiconductor distributed Bragg reflector mirror layer and has an opening to extract light from said semiconductor light-emitting layer, a first electrode formed around said light extraction section on said second semiconductor distributed Bragg reflector mirror layer, a second electrode formed on said second main surface of said substrate, and a reflector portion provided on an inner wall of a groove, said groove being formed by removing portions of said first semiconductor distributed Bragg reflector mirror layer, said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer which lie in a peripheral portion of said first electrode and formed to penetrate through each of said semiconductor light-emitting layer and said second semiconductor distributed Bragg reflector mirror layer and reach said first semiconductor distributed Bragg reflector mirror layer, said reflector portion being formed to reflect part of light emitted from said semiconductor light-emitting layer into said groove; and an optical fiber on which light from said light extraction section and said groove of said resonant-cavity light-emitting diode is incident.
 15. The optical transmission module according to claim 14, wherein said groove of said resonant-cavity light-emitting diode is configured in substantially a ring form and a diameter of a light-receiving end surface of said optical fiber is larger than that of said ring of said ring-form groove.
 16. The optical transmission module according to claim 14, wherein said reflector portion of said groove of said resonant-cavity light-emitting diode is configured with a concave surface with respect to light from said semiconductor light-emitting layer.
 17. The optical transmission module according to claim 14, wherein said reflector portion includes a reflection film which is formed on an inner wall portion of said groove and reflects light from said semiconductor light-emitting layer.
 18. The optical transmission module according to claim 14, wherein said semiconductor light-emitting layer of said resonant-cavity light-emitting diode includes an active layer using an In_(1−x)(Ga_(1−y)Al_(y))_(x)P-series material (0≦x, y≦1) and a light emission wavelength thereof is 620 to 690 nm.
 19. The optical transmission module according to claim 14, further comprising a high-resistance region which is formed to reach said inner wall of said groove and formed by making portions of said first semiconductor distributed Bragg reflector mirror layer and said second semiconductor distributed Bragg reflector mirror layer of said resonant-cavity light-emitting diode other than at least portions thereof which lie just below said opening of said light extraction section electrically highly resistive.
 20. The optical transmission module according to claim 19, wherein each of said first semiconductor distributed Bragg reflector mirror layer and said second semiconductor distributed Bragg reflector mirror layer of said resonant-cavity light-emitting diode includes a semiconductor layer with a high Al composition ratio and said high-resistance region is formed by selectively oxidized part of said semiconductor layer in a lateral direction from said groove. 